Molecular Design Strategies for High-Voltage Organic Cathodes

Abstract

Organic electrode materials (OEMs) offer promising pathways toward sustainable and high-performance rechargeable batteries, yet their practical implementation is limited by rigid crystal structures, poor electronic conductivity, and low redox potential. Here, we conduct a systematic molecular-level investigation of two organic cathodes, phenazine-1,4,6,9-tetrone (PzTO) and dithiin-fused naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) (DNP), through a combined computational and experimental approach. Solution-phase cyclic voltammetry reveals a substantial redox potential gap between them, with DNP exhibiting a reduction potential ∼500 mV higher than PzTO. This difference becomes more pronounced in solid state measurements, where the first reduction potentials reach ∼3.68 V vs. Li⁺/Li for DNP and 3.08 V for PzTO. By dissecting the molecular origins of these trends, we identify two governing features: (i) changes of aromaticity upon reduction (differential aromaticity) and (ii) Li–O coordination number. Density functional theory calculations confirm that these features strongly modulate lithiation free energies. Extending our analysis to a series of hypothetical derivatives of PzTO and DNP, we establish a linear relationship between differential aromaticity and lithiation free energy and show that the introduction of additional Li–O coordination enhances redox potentials. Taken together, these molecular engineering insights offer a mechanistic foundation for rationalizing high-voltage performance and guiding the design of next-generation OEMs.